Hobart 120CU20, Operation And Maintenance Manual With Illustrated Parts List

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OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 1-1
Page 22
9) Power Module Panel Assembly.
The power module panel assembly, sometimes referred to as the contactor panel, is located at the left
front of the machine under the control box. The panel assembly provides a means of connecting and
disconnecting generator output to and from the load (aircraft).
a) Load contactor(s)
The load contactor(s) each contain a magnetic operating coil and four sets of contacts. The three
larger contacts conduct three-phase AC generator output. A small contact set is connected to the
Digital Control PC Board (CTL) to activate the protective monitor circuit. Three-phase, 400-Hz
generator output power is conducted to the load contactors by 2/0 cables that pass through current
transformers
.
b) Current transformers (CT1-CT6)
On each individual output a set of current transformers are used to monitor and control the line-drop
compensation, ammeter, and overload circuit.
(1) Line-Drop Compensation
The current transformers detects the magnitude and power factor of current flowing from
generator to load. They feed a signal to the voltage regulator that interprets the signal and alters
the exciter field current as required to maintain a constant predetermined voltage at the load.
(2) Ammeter
The current transformers convert a current signal to a voltage signal, which is sent to the Voltage
Regulator PC Board (REG). The ammeter is really a voltmeter graduated and numbered in
amperes to show current proportional to the voltage signal received.
When there is overload on the output for more than 5 minutes (load exceeding 326 amperes per
output or 125% of rated load), the main overload sensing circuit sends signals the load the
contactor(s) circuit to open both load contactors.
(3) Overload, No 1 and/or No. 2 output
On each individual output the current transformers converts a current signal to a voltage signal.
The voltage signal is sent to the ammeter and to the overload monitoring circuit for that output.
The overload monitoring circuit will open the contactors when the output current reaches 125% of
the normal rated output current. The monitoring circuit moniters each individual output, as well
as, the overall current for a dual output machines.
The following is a list of overload module characteristics:
•
At 125% load the module will function in 5 minutes.
•
At 150% load the module will function in 30 seconds.
•
AT 200% load the module will function in 10 seconds.
NOTE: The overload protective system will function when any phase carries 123% to 127% of
rated load. All times are plus or minus 25% and are non-adjustable.